The present invention is concerned with down hole motors and methods of their operation.
Down hole motors are commonly used in drilling applications, particularly in long reach drilling where the drill string length is considerable. In oil well drilling applications, the drill string length may exceed 10,000 m. However, problems exist when the wells are not vertical.
In general, down hole motors are hydraulically driven by the drilling mud/fluid.
There are several instances when it may be desirable to circulate the drilling fluid while drilling is not actually taking place. These include, amongst things, withdrawal of the bit/motor and flushing out debris. If during these operations, the drill bit turns, it will dig in to the low side of the hole, resulting in a hole which is oval shaped. This is highly undesirable since it can lead to side tracking and the failure of completion devices.
A solution to these difficulties is to provide a bypass valve for the drilling liquid so that it can circulate without turning the motor. Various proposals have been made, in particular, systems where a motor bypass valve is activated in response to pressure pulses. Unfortunately, the pressure fluctuates constantly during normal drilling and so in practice, these systems have not met with success.
It is therefore an object of the present invention to provide a system for a down hole motor which can be activated with greater certainty by the drill operator, to enable the drilling fluid to circulate through the bit without turning the drill bit.
According to one aspect of the invention, there is provided a method of operating a down hole motor assembly which comprises a hydraulic drive portion, a drill bit operatively connected to the drive portion, and a disengage mechanism arranged to disengage drive to the drill bit, the method comprising: supplying fluid to the drive portion at a first fluid flow rate selected to drive the drive portion and consequently the drill bit; supplying fluid at a second flow rate which is greater than the first flow rate, thereby actuating the disengage mechanism so that the drill bit ceases to be rotated; and supplying fluid at a third flow rate which is significantly lower than the first flow rate, thereby resetting the disengage mechanism so that drive is reconnected to the drill bit.
Generally, a down hole motor is arranged to run at an optimum speed and drilling fluid is pumped to the motor at the appropriate flow rate to achieve that speed. If the motor is run at a higher speed for any length of time, the motor will suffer damage. However, the motor can be run at a high speed for a short period without significant damage. In the present invention, an increased flow rate is used, but only for a short period. The advantage is that it is very much easier for an operative to control drilling fluid flow rate than pressure and, mechanisms which are sensitive to flow rate changes are more reliable than mechanisms sensitive to pressure changes.
Typically, during normal drilling, a drilling fluid flow rate might be 2000 l/min. This would correspond to the first flow rate. The second flow rate used, might then be about 2500 l/min. Preferably, the second flow rate is greater than the first flow rate by 10% to 50%, more preferably from 15% to 30%, for example, about 20%. Preferably the third flow rate is at most 10% of the first flow rate, more preferably at most 5% and is most preferably zero.
Preferably, the fluid at the second flow rate, moves a disengage component axially, thereby actuating the disengage mechanism. Preferably, the fluid is passed through a nozzle which, at the second flow rate moves axially, thereby causing the disengage component to move. Preferably, the fluid drives a centrifugally operated actuating component at the second flow rate, in order to release the disengage mechanism for actuation. Alternatively, the disengage mechanism is actuated by means of a closed hydraulic system which is itself responsive to the fluid flow rate.
Preferably, the stop of actuating the disengage mechanism comprises directing the fluid along a bypass path which bypasses the drive portion. Alternatively, the step of actuating the disengage mechanism comprises disengaging a gear connection between the drive portion and the drill bit. Preferably, the step of re-setting the disengage mechanism comprises moving back the disengage component to its former position.
According to another aspect of the invention, there is provided a down hole motor assembly which comprises an hydraulic drive portion, a drill bit operatively connected to the drive portion and a disengage mechanism arranged to disengage drive to the drill bit; the disengage mechanism being arranged to be actuated by supplying fluid to the drive portion at a second flow rate which is greater than a first flow rate at which fluid is supplied to run the drive portion during normal drilling; the disengage mechanism being arranged to be re-set so that drive is reconnected to the drill bit when fluid is supplied to the drive portion at a third flow rate which is significantly lower than the first flow rate.
Preferably, the assembly includes a disengage component which is axially movable to actuate the disengage mechanism and preferably, a nozzle operatively connected to the disengage component, through which the fluid is arranged to flow. There is preferably also a centrifugally operated actuating component arranged to release the disengage mechanism for actuation when the actuating component is driven by the fluid at the second flow rate. In a preferred embodiment, the actuating component comprises a series of fingers pivotally connected to a housing which is rotatable by the fluid flow. The actuating component may be driven by the drive portion or by an independent drive mechanism operable by the fluid flow.
FIG. 2c is an enlarged view of the bypass actuator mechanism;
FIGS. 3a and 3b are similar to FIGS. 1a and 1b, but show a third embodiment;
FIG. 3c is an enlarged view of the actuator mechanism;
FIGS. 4a and 4b are similar to FIGS. 1a and 1b, but show a fourth embodiment;
FIG. 4c is a section on line Axe2x80x94A in FIG. 4a; 
FIG. 4d is a section on line Bxe2x80x94B in FIG. 4a; 
FIGS. 5a and 5b are similar to FIGS. 1a and 1b but show a fifth embodiment; and
FIG. 5c is a section on line Axe2x80x94A in FIG. 5b. 
Preferably, the disengage mechanism is a fluid bypass valve operated by the disengage component which allows the fluid to bypass the drive portion when the fluid is supplied at the second flow rate. Alternatively, the disengage mechanism is a clutch arrangement operated by the disengage component to disengage the drill bit from the drive portion when the fluid is supplied at the second flow rate. Conveniently, the clutch arrangement is located between the drive portion and the drill bit.
Preferably, the assembly includes means for returning the disengage component to a former position to reset the disengage mechanism, for example, a spring. The assembly may also include a locking mechanism for locking the disengage mechanism in its actuated configuration. Preferably, the locking mechanism comprises a pin in the disengage component which is arranged to engage a detent in a fixed part of the assembly. Preferably, the pin is arranged to be disengaged when the fluid flows at the third flow rate.